Inflatable safety restraint systems are incorporated into automobiles and other vehicles to protect occupants in the event of a crash. An inflatable safety restraint system includes an airbag module incorporating an inflator and an airbag cushion, wherein the inflator provides inflation gas for inflating and deploying the airbag cushion.
Hybrid inflators provide the inflation gasses from a combination of stored pressurized gas and combustible material which is ignited to heat and expand the stored pressurized gas, and which may provide additional inflation gas as a product of combustion. The combustible material is often a pyrotechnic but may also be a liquid fuel. The products of combustion are delivered to the stored gas chamber to heat and expand the stored gas therein. It is further typical that the combustion chamber for the combustible material be located within the stored gas chamber, in order to provide heat transfer to the stored gas and further provide a relatively compact structure. Passenger side inflators often have an elongated tubular housing and a common variant has the combustible material at the closed end thereof with an initiator means mounted through the closed end and inflation gasses delivered from the open end of the elongated housing. Prior to operation of the inflator, the open end is sealed by a rupturable diaphragm, and the rupturable diaphragm is opened by internal pressure created when the combustible material is ignited. Alternatively, a mechanical linkage can be provided to puncture the seal. In inflators which are opened by increased internal pressure within the gas storage chamber, the need to develop high internal pressures necessary to release inflation gasses dictate a substantial housing. This increases the weight and cost of the inflator. The alternative of opening the inflator by mechanical linkage also requires additional cost and weight of the mechanical components.
The same considerations apply to a driver's side inflator, in which the combustible material is generally provided in a center tie surrounded by a toroidal gas storage chamber, with the gas being delivered through a burst disk or frangible portion of the housing on the end of the center tie facing the airbag cushion.
For efficient heating of the stored gas, it is also beneficial to have the combustion chamber and the outlets therefrom in the path of inflation gasses exiting the inflator, i.e., near the outlet burst disk. Such an inflator is shown in U.S. Pat. No. 5,131,680, wherein a projectile is fired through the burst disk to initiate a primer for igniting a combustible material contained in a combustion chamber near the outlet end of the inflator. Such prior art hybrid inflators require a substantial number of precision parts to function in their intended manner, thereby increasing the difficulty of manufacture and attendant cost.
All of these structures are somewhat more heavy, more complex and more expensive to manufacture than is desirable and, accordingly, there is a need for an improved hybrid inflator.